4) Tim ne N* sao cho: 2° + 2" + 2" = a?
-2^8 + 2^11 + 2^n + a^2
=>2n=α2−(28+211)=a2−48=(a+48)(a−48)=>2n=α2−(28+211)=a2−48=(a+48)(a−48)
+Đặt:n=p+q+Đặt:n=p+q Ta có: a−48=2na−48=2n
=>[a−48=2qa+48=2p[a−48=2qa+48=2p=>2p−2q=962p−2q=96
⇔ 2^q ( 2^p-a - 1 ) = 2^5 . 3
Vì ( 2^p-q - 1 ) lẻ nên: q−5=>p−7=>n−12q−5=>p−7=>n−12
-C2
4,2∧8+2∧11+2∧n=a∧2
=256+2048+2∧n=a∧2
=2304+2∧n=axa
⇒n=12
Bài 7 trong hình :
